Method for forming dye image using an electrophotographic developer containing a gelatin toner

ABSTRACT

A color printing process which comprises the steps of (1) processing with an acid an electrophotographic sensitive layer of a photoconductor mainly consisting of photoconductive zinc oxide, the layer having a gelatin image prepared by forming an electrostatic latent image on the layer and then converting the latent image into the gelatin layer by processing with an electrophotographic developer containing fine particles of gelatin, whereby the zinc oxide contained in the electrophotographic sensitive layer is removed, (2) bringing the gelatin layer into contact with a solution of a dye in a solvent mainly consisting of water to provide the dye to the gelatin image, (3) rinsing the layer with acid water to remove the excessive solution of the dye wetting the gelatin image, whereby the dye is once insolubilized, and (4) bringing the dyed gelatin image into contact with a layer capable of being readily dyed by the dye to transfer the dye onto the layer.

United States Patent Tamai [151 3,654,865 1451 Apr. 11,1972

DEVELOPER CONTAINING A GELATIN TONER [72] lnventor: Yasuo Tamai, Asaka, Japan [73] Assignee: Fuji Photo Film Co., Ltd., Kanagawa,

Japan [22] Filed: Feb. 5,1970 [21] Appl. No.1 9,077

[30] Foreign Application Priority Data Feb. 5, 1969 Japan ..44/8518 [56] References Cited UNITED STATES PATENTS 3,001,872 9/1961 Kurz ..96/1 2,952,536 9/1960 Kurz ...l01/463 2,297,691 10/1942 Carlson ..96/1.4 3,428,453 2/1969 Honjo ..l0l/40l.lX

Primary Examiner-Robert E. Pulfrey Assistant Examiner-R. T. Rader Attorney-Addams & Ferguson ABSTRACT A color printing process which comprises the steps of (1) processing with an acid an electrophotographic sensitive layer of a photoconductor mainly consisting of photoconductive zinc oxide, the layer having a gelatin image prepared by forming an electrostatic latent image on the layer and then converting the latent image into the gelatin layer by processing with an electrophotographic developer containing fine particles of gelatin, whereby the zinc oxide contained in the electrophotographic sensitive layer is removed, (2) bringing the gelatin layer into contact with a solution of a dye in a solvent mainly consisting of water to provide the dye to the gelatin image, (3) rinsing the layer with acid water to remove the excessive solution of the dye wetting the gelatin image, whereby the dye is once insolubilized, and (4) bringing the dyed gelatin image into contact with a layer capable of being readily dyed by the dye to transfer the dye onto the layer.

3 Claims, No Drawings METHOD FOR FORMING DYE IMAGE USING AN ELECTROPHOTOGRAPHIC DEVELOPER CONTAINING A GELATIN TONER This invention relates to the color printing process having its basis on the recording method such as electrophotographic method or electrostatic recording method which utilizes electrostatic latent image. More particularly, it relates to improvements in the dye transfer process whereby the electrostatic latent image is developed and coverted into a gelatin image and the resultant gelatin relief is utilized.

For obtaining color prints of good quality, there are widely employed two methods. One of the methods combines silver halide emulsions with the color developing process and this has gained the widest acceptance.

The other method is the dye transfer process whereby the tanning development is accomplished by means of a silver halide emulsion and the gelatin relief obtained consequently is utilized for transfer. These methods have both been popularized such as in Technicolor system.

Now the two methods described above are compared. The former method is suitable for mass production. However, the image to be obtained thereby sufiers from insufficiency of durability. In contrast thereto, the latter method (dye transfer process) can give images of good quality having extremely high durability. This dye transfer process rather approaches to printing. For this reason, this process proves to be more economical when it is used for obtaining a larger number of duplicates from one original. However, it is not suitable for purposes of making a small number of duplicates, for the cost per duplicate will be considerably higher in this case. The reason is that the preparation of gelatin relief to be used as the original plate consumes time and calls for skill.

An object of the present invention is to provide a method for obtaining color prints inexpensively and easily. Another object of the invention is to provide improvements in the dye transfer process utilizing the gelatin relief which is produced by means of electrophotography.

A still further object of the invention consists in providing a method for obtaining a clear color image having high image density by the dye transfer process which makes use of gelatin relief produced by means of either electrography or electrostatic recording method.

The present invention is directed to a color printing process, which comprises (1) processing with an acid an electrophotographic sensitive layer of a photoconductor mainly consisting of photoconductive zinc oxide, said layer having a gelatin image prepared by forming an electrostatic latent image on the layer and then converting said latent image into the gelatin layer by processing with an electrophotographic developer containing fine particles of gelatin, whereby the zinc oxide in said layer is removed, steps of: (2) bringing said gelatin image into contact with solution of a dye in a solvent mainly consisting of water to provide said dye to the gelatin image, (3) rinsing said layer with acid water to remove the excessive dye solution wetting said gelatin image, whereby the dye is once insolubilized, and (4) bringing said dyed gelatin image into contact with a layer capable of being readily dyed with the dye to transfer said dye onto said layer.

The aforementioned color printing process of the present invention comprises the following steps of treatment, for example,

I. The electrophotographic sensitive layer containing therein zinc oxide is electrically charged in the dark and then exposed to light projected through an image, whereby an electrostatic latent image is formed thereon.

II. The sensitive layer now carrying thereon the electrostatic latent image is treated with the electrophotographic developer containing therein gelatin toner (such as electrophotographic liquid developer containing gelatin toner in a carrier liquid) so as to develop the image.

Ill. The gelatin image thus obtained is fixed and hardened by a suitable method.

IV. The zinc oxide and other photoconductive element soluble in acid which are present in the electrophotographic sensitive layer are removed by treating with an acid.

V. The aqueous solution of a water-soluble dye is brought into contact with the gelatin image so as to provide the dye to the image.

VI. Then the excessive dye solution adhering to the gelatin relief is removed by washing with acid water.

Vll. A sheet possessed of a surface layer capable of readily receiving the aforementioned dye is brought into contact with the gelatin image. At this time, thedye transfers it self onto the dye-receiving layer to produce a final color image on the sheet.

By repeating the steps of (V), (VI), and (VII) on one and the same gelatin relief, many sheets containing dye image can be produced.

The color printing process of the present invention mentioned above is characterized by incorporation of such step of treatment as shown in (IV), namely, the step for removing acid-soluble photoconductive elements (such as zinc oxide) contained in the electrophotographic sensitive layer by means of an acid.

If the only aforementioned step of (IV) is omitted from the whole course of steps (I) through (VH), the final color image to be obtained will suffer from low optical density and insufficient clearness of image.

By substantially completely removing the acid-soluble photoconductive elements (such as zinc oxide) present in the electrophotographic sensitive layer prior to the adsorption of dye on the gelatin image as is effected in the present invention, it has now become possible to prevent the dye, adsorbed in the previous step of (V), from being released in the aforementioned step of (VI), namely, the step in which the excessive dye solution adhering to the gelatin relief is washed off. This is believed to result from the following cause.

The water-soluble dye to be used in the dye transfer process is either an acid dye or a mordant dye. In an acid solution an acidic dye generally has its solubility decreased. In the aforementioned step of (V), therefore, the excessive dye solution adhering to the gelatin relief is removed and the dye in the gelatin image is fixed when the dye solution is brought into contact with the gelatin relief to cause the dye to be adsorbed and subsequently the gelatin relief is washed with acid water.

However, when a sensitive layer containing therein such photoconductive element as zinc oxide exists beneath the gelatin image, the neighborhood of the surface of the sensitive layer always becomes weakly basic.

This fact can be confirmed by carrying out the experiment such as is described below.

When several grams of zinc oxide is placed in ml. of distilled water and agitated, the solution is found through measurement to have a pH value of 7.8. It is difficult to have this pH value of the dispersion changed by addition of acid or base. The reason is that so long as there exists an excess of zinc oxide, the zinc oxide functions as the buffer agent. Thus, it is considered the surface close to the sensitive layer containing therein zinc oxide always assumes weak basicity.

Therefore, even when the gelatin relief is washed with acidic water subsequent to allowing the gelatin image to adsorb the dye, the neighborhood of the gelatin image cannot be acidified sufficiently. Consequently, the dye which has been once adsorbed is dissolved out infinitely even when the washing is made in an acidic cleaning bath. As a result, the concentration of the dye absorbed in the gelatin image portion is lowered, so that the image obtained after the dye transfer has a low density. Also, since the dye continues to be dissolved out of the gelatin image portion including dye into the adjoining area, the image obtained after the dye transfer is deprived of its clearness.

These difficulties can be overcome all at once by removing from the electrophotographic sensitive layer zinc oxide and other acid-soluble photoconductive materials as is accomplished by the present invention. For the purpose of removing zinc oxide and acid-soluble photoconductive materials from the sensitive layer, there are used various acids in the form of aqueous solution. For example, there can be used such inorganic and organic acids as nitric acid, acetic acid, hydrochloric acid, and sulfuric acid which can dissolve zinc oxide. Of these acids, acetic acid proves to be most suitable. Although zinc oxide can be removed by alkalis, alkalis are not desirable because they tend to destroy the gelatin image. It is conceivable that the insulating resin contained in the sensitive layer may impede the elution while zinc oxide is removed by such acid. In the case of the electrophotographic sensitive layer having photoconductive zinc oxide as the principal photoconductive element (generally having more than 70 parts by weight of zinc oxide contained in 100 parts by weight by photoconductive elements as a whole) such as is used by the present invention, since zinc oxide is contained in a considerably large quantity, substantially all zinc oxide particles exist in mutually contacting state or a state approaching thereto in the photosensitive layer. Therefore, zinc oxide can be removed easily even while there exists the insulative resin for combination in the photosensitive layer. It does not matter whether such zinc oxide particles as are unremovable exist isolated in the resin and remain therein after the treatment with acid. The reason is that such zinc oxide particles cannot exert any obstructive activity either in the step of absorption of dye by the gelatin image or in the step of washing with acidic solution.

As mentioned above, the electrophotographic sensitive material to be used for the present invention uses zinc oxide as the principal photoconductive element and forms on a base a sensitive layer consisting of such photoconductive element and in insulative resin. According to the method of this invention, since the electrophotographic sensitive material undergoes the treatment with acid as mentioned above for the purpose of removing zinc oxide therefrom, the base is desired to be resistant to water and to acid. For use as the base, particularly suitable are cellulose triacetate film, polyethylene terephthalate film, polycarbonate film and the like. Generally, a low electric resistance layer is formed ordinarily between the sensitive layer as mentioned above and the base.

It is therefore proper to select a low electric resistance layer of the type which is not corroded by the aforementioned acid treatment.

The acid to be used in the aforementioned step of (IV) is desired to have a concentration exceeding 5 percent by weight, though variable with the kind of acid. The upper limit of the concentration of the acid is determined by the kind of acid, the acidproofness of the base and the low electric resistance layer of the electrophotographic sensitive material to be used, and the acidproofness of the gelatin image. Generally, consideration must be paid to the fact that while the dissolving power of a given acid against zinc oxide increases with the concentration of that acid, the dissolving power of the acid against zinc oxide declines as the acid concentration rises extremely high.

When an acetic acid solution is used for the aforementioned acid treatment, for example, the concentration of the acetic acid is suitable in the range of from 8 to 50 percent by weight.

It is suspected that when zinc oxide is removed from the sensitive layer carrying thereon the gelatin image, the gelatin image may be broke. In actuality, however, it has been found that such destruction of image does not occur at all. Rather, the portion containing the gelatin image proves to be stabler mechanically.

For use in the present invention, acidic dyes and mordant dyes are suitable. Specific examples of such dyes are as follows.

Cyan dyes: acid blue 45, acid green 16, acid green 1, acid blue 1, acid blue 9, and acid blue 54.

Magenta dyes: acid red 80, acid red 34, acid red 1, acid violet 19, and acid violet 7.

Yellow dyes: acid yellow 23, acid yellow 1 1, acid yellow 12, and acid yellow 34.

The image to be obtained by the present invention has very high quality, high resistance to light, and excellent color quality. Since this image has no surface reflection compared with the image obtainable electrophotographically by using toners of different colors, it reproduces colors with depth.

Further, since individual colors which form the multicolor image are highly transparent, they mix with one another perfectly and reproduce the original color faithfully.

The image which is obtained once can produce images by dye transfer so far as the image is replenished with dye. Thus, the image can produce many prints.

The present invention is advantageous for the electrophotographic sensitive layer using zinc oxide as the photoconductive element. It is similarly advantageous for the photoconductive layer combining zinc oxide with other photoconductive elements. The photoconductive elements which are thus used in combination with zinc oxide include Cds, CdSe, Cd(S, Se), ZnS, ZnSe, and TiO Some of these photoconductive elements can be removed, together with zinc oxide, from the sensitive layer by means of acid, and others, if suffered to remain in the sensitive layer, do not impede the step of dye transfer.

A more specific description is given of the present invention by referring to preferred embodiments.

EXAMPLE 1 Five grams of photographic gelatin was added to g. of distilled water. The gelatin became impregnated with water 30 minutes later. This was heated to 60 C to give rise to a clear water solution of gelatin.

While 10 ml. of this aqueous solution of gelatin was kept at 45 C, methanol was added thereto until white haze occurred slightly therein. The quantity of methanol thus added totalled 11 ml. Then 0.5 ml. of distilled water was added thereto to eliminate the white haze. Thus, there was obtained a solution of gelatin in a mixed solvent of water and methanol. The solution in its entire quantity was dispersed in the solution of the following composition by means of ultrasonic stirring.

980 ml. 20 ml.

Acetone Cotton seed oil Varnish prepared by cooking rosinmodified phenolformaldehyde resin with linseed oil Toluene 3 ml. 36 ml.

The resin component of this varnish was insoluble in acetone and soluble in the carrier liquid.

On addition, aggregates of the resin were observed to form within the liquid. After the aggregates had substantially settled over the subsequent 30 minutes, the supernatant was removed by decantation. The 800 ml. of acetone was added to the sediment and agitated. After 15 minutes of standing thereafter, the supernatant was removed again by decantation to obtain 200 ml. of liquid containing therein the sediment. This liquid was treated with a centrifugal separator to produce a sediment of resin containing therein fine particles of gelatin. The sediment in its entire quantity was combined with a mixed solvent having the following composition and then agitated.

Toluene 20 ml. Xylene 3.5 ml. Cotton seed oil 6 ml. Nonionic surfactant solution 0.3 ml.

The sediment could be dissolved substantially completely by agitation to give rise to a viscous gelatin dispersion having a yellowish white color. The liquid was a concentrated dope of liquid developer and could be preserved for a long time.

1600 ml. 400 ml.

Cyclohexane Kerosene Thus was obtained an electrophotographic liquid developer assuming a lightly milky white color.

Kerosene was added for the purpose of lowering the rate at which the liquid developing agent evaporates. The gelatin toner within the liquid developing agent was found to have positive electric charge.

Separately, 100 parts by weight of photoconductive zinc oxide and 20 parts (parts being given by weight hereinafter) of epoxy ester of dehydrated castor oil fatty acid were mixed with a suitable quantity of toluene to produce a homogeneous coating mixture. To this mixture, there was added a solution prepared by dissolving 20/ 100 part of fluorescein and 20/100 part of tetrabromophenol blue in a small quantity of ethyleneglycol monomethyl ether, so as to extend the photoconductive response of zinc oxide to almost whole range of visible spectrum. After further addition of a suitable quantity of toluene, the mixture was coated on a polyethyene terephthalate film (90p. in thickness) having aluminum vacuum deposited thereon. The dry thickness was about 8p. The product, when dried sufficiently in a dark place, functioned satisfactorily as electrophotographic sensitive sheet.

This electrophotographic sensitive sheet was exposed to corona discharge in a dark place to have its surface negatively charged uniformly. Then a color slide selected as to the original was mounted on an enlarger, with a red filter set on the slide. The negatively charged sensitive sheet was exposed to light projected through the original.

The sensitive plate which had undergone the exposure was wetted with kerosene and immediately soaked in the liquid developer mentioned above. In this case, a stainless steel tray was used as the container, so that the tray could play the part of developing electrode when the surface of latent image was brought close to the tray bottom. After about 90 seconds of standing therein, the sheet wax removed from the bath, washed with iso-paraffin (Isoper E made by Esso Standard Oil Co.), and then dried.

Then the sheet which had undergone the developing treatment was soaked in 1 percent methanol solution of formaldehyde, allowed to stand at rest overnight at room temperature, and then treated so as to harden the gelatin image.

Consequently, there was obtained a sensitive layer carrying thereon the gelatin image.

For the purpose of removing zinc oxide from the sensitive layer, there was prepared a solution of the following composition.

In this solution, the sensitive sheet carrying the gelatin image was soaked. The solution was agitated occasionally. Two minutes later, it was observed that zinc oxide was removed from the surface of the sensitive layer and the entire surface assumed a metallic gloss because of the aluminum layer formed below the sensitive layer.

Subsequently, the sheet was washed sufficiently in distilled water. Finally, the sheet was soaked in methanol, removed from methanol, and dried in a forced current of hot air.

As the result of the preceding treatments, there was obtained a gelatin relief for cyan printing.

By following the same procedure, another sensitive sheet was exposed to light projected through the same original combined with a green filter, subjected to the same developing treatment, to obtain a relief for magenta printing. Similarly, a matrix for yellow printing was obtained by combining the original with a blue filter.

The three gelatin reliefs were soaked for 2 minutes in the aqueous solution of acid blue 54, acid violet 7, and acid yellow 23 respectively, removed from the solutions, and washed in a bath incorporating therein acetic acid. The excessive dye solution adhering to the sheet was removed by this treatment. However, it is completely recognized the phenomenon so that the dye absorbed in the gelatin image portion may melt out into the cleaning bath.

In the meantime, a sheet possessed of a gelatin layer was soaked in aluminum sulfate solution mordanted, and registered to and pressed against the three gelatin reliefs one after another.

Through this treatment, the dye absorbed in each of the toner images was transferred onto the gelatin layer. Thus was obtained a duplicate having extremely high product quality. These gelatin relief could withstand about repeated uses completely.

EXAMPLE 2 The procedure of Example 1 was followed, except 20 parts by weight of epoxy ester of dehydrated castor oil fatty acid serving as the insulative binding agent for the photoconductive zinc oxide was substituted by 20 parts by weight of copolymer of vinyl chloride with vinyl acetate to form the sensitive layer. In this blending, a suitable quantity of acetone was used in the place of toluene.

By the same operation as used in Example 1, zinc oxide could be removed from the sensitive layer by use of acetic acid solution. When the gelatin relief obtained in this example was made to absorb acid violet 7 and the dye transfer was carried out, the maximum optical density of the image was 2.16.

In the present example, when the gelatin relief was soaked in a washing bath after the step of absorption by the gelatin image of the dye, no phenomenon of elution of the said dye from the gelatin image portion was observed at all.

COMPARATIVE EXAMPLE In the procedure of Example 2, the treatment for removal of zinc oxide was omitted, and the sheet which had undergone the treatment for fixing the image was soaked in the solution of acid violet 7 to allow the gelatin image to absorb the said dye.

Subsequently, the sheet was soaked in an acetic acid cleaning bath. When it was washed therein, it was found that the dye continued to be aluted from the gelatin image portion.

Therefore, the washing treatment was discontinued before completion and the dye transfer was carried out.

The image thus obtained lacked cleamess, with the maximum optical density being 1.80.

These troubles arose because before dye transfer the dye including in the gelatin image portion was not sufficiently nonsoluble (fixing).

EXAMPLE 3 In the procedure of Example 1, 14 percent nitric acid was used in place of the aqueous solution of acetic acid for the removal of zinc oxide. By following the same procedure as in Example 1, there were obtained gelatin reliefs. In the present process, the aluminum layer vacuum deposited on the sheet withstood nitric acid of the aforementioned concentration. These gelatin reliefs were employed for color printing in the same way of dye transfer as in Example 1, to produce satisfactory results.

EXAMPLE 4 The procedure of Example 1 was followed, except 1.5N hydrochloric acid was used for the removal of zinc oxide in the place of acetic acid. Thus were obtained gelatin reliefs. The aluminum layer vacuum deposited on the plate withstood the treatment for removal of zinc oxide using hydrochloric acid of the aforementioned concentration.

When the dye transfer treatment was carried out on the gelatin matrixes prepared in this example, there was obtained a color image having the came clearness as in Example 1.

EXAMPLE In the procedure of Example 1, 3.5N sulfuric acid was used in the place of acetic acid for the removal of zinc oxide. By following the procedure of Example 1 otherwise, there were obtained gelatin reliefs. The aluminum layer withstood the treatment for removal of zinc oxide by means of sulfuric acid of the aforementioned concentration.

EXAMPLE 6 In the procedure of Example 1, the development of image was carried out by employing a cascade developer containing therein gelatin toner having the average particle size of 12 instead of using the liquid developer containing therein gelatin toner. The toner had positive polarity.

After the step of development, gelatin was fixed by exposing the sheet surface to a forced current of steam. Thereafter, the

1. image exposing an electrically charged electrophotographic sensitive layer containing zinc oxide to form a latent electrostatic image;

2. treating said sensitive layer with an electrophotographic developer containing a gelatin toner to develop said electrostatic latent image;

3. fixing said gelatin image to thereby form a gelatin relief image on said electrophotographic sensitive layer;

4. treating said sensitive layer with its gelatin relief image with an acid to remove said zinc oxide from said electrophotographic sensitive layer;

5. contacting said gelatin relief image with a solution of a dye mainly in a solvent consisting of water to allow the dye to be absorbed by'the gelatin relief image, excessive dye also being deposited on said relief image;

6. washing said gelatin relief image with acid water to thereby remove the said excessive dye solution adhering to the gelatin relief image without removing the dye absorbed by the gelatin relief image; and

7. contacting said gelatin relief image with a sheet having a surface layer capable of receiving said dye to thereby transfer said image to said receiving sheet.

2. The process as claimed in claim 1 wherein said acid is selected from the group consisting of acetic acid, nitric acid, hydrochloric acid and sulfuric acid.

3. The process as claimed in claim 1 wherein said electrophotographic sensitive layer is formed on a film comprising a material selected from the group consisting of cellulose triacetate, polyethylene terephthalate and polycarbonate. 

2. treating said sensitive layer with an electrophotographic developer containing a gelatin toner to develop said electrostatic latent image;
 2. The process as claimed in claim 1 wherein said acid is selected from the group consisting of acetic acid, nitric acid, hydrochloric acid and sulfuric acid.
 3. The process as claimed in claim 1 wherein said electrophotographic sensitive layer is formed on a film comprising a material selected from the group consisting of cellulose triacetate, polyethylene terephthalate and polycarbonate.
 3. fixing said gelatin image to thereby form a gelatin relief image on said electrophotographic sensitive layer;
 4. treating said sensitive layer with its gelatin relief image with an acid to remove said zinc oxide from said electrophotographic sensitive layer;
 5. contacting said gelatin relief image with a solution of a dye mainly in a solvent consisting of water to allow the dye to be absorbed by the gelatin relief image, excessive dye also being deposited on said relief image;
 6. washing said gelatin relief image with acid water to thereby remove the said excessive dye solution adhering to the gelatin relief image without removing the dye absorbed by the gelatin relief image; and
 7. contacting said gelatin relief image with a sheet having a surface layer capable of receiving saId dye to thereby transfer said image to said receiving sheet. 